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How a green fish farm is changing the salmon industry – drop by drop

Photo: Danish Salmon moves fish to bigger tanks as they grow. The company reuses 99% of the water in its tank system, a Danish aquafarming pioneer.

Denmark_Hirsthals

Sustainable Salmon

The village of Hirtshals, located on the northwest coast of Denmark on the North Sea, bustles with deep sea fishing boats, markets, tourists and fish auctions. It is one of the old, established Danish fishing communities.

Just up the hill from the harbour inside a large, non-descript building, a Scandinavian salmon supplier is doing something unique. The company not only raises its fish in tanks, but it recirculates more than 99 percent of the water in a closed system. Danish Salmon’s plant saves vast amounts of water – as well as corresponding energy for pumping fresh water from the sea. It also reduces waste material discharge and helps to prevent fish exposure to parasites and other predators.

Land-based aquaculture – fish farming – is not new, but the Danish Salmon is one of the first in the world to grow salmon in a full life cycle from fertilised eggs to harvest size of 4-6 kg (8-13 lbs). It’s also the biggest, fully recirculating aquaculture system (RAS) for commercial use.

Photo: You don’t need to be next to the sea for a land-based aquaculture system with recirculation technology, says Mark Russell, plant manager, Danish Salmon.

Mark Russell

Like water for blood

“We aim to produce more than 2,000 tonnes of harvest-size fish per year with land-based recirculation technology at its core. We are kind of pioneers in this area at the moment,” says Mark Russell, plant manager at Danish Salmon.

Russell says recirculation systems can be placed almost anywhere as long as there is a water supply. “You don’t need to be right next to the sea,” he says. “You could put them next to your marketplace, basically – in New York or London – as long as you have a water supply and an ability to remove the water as well.”

Another main advantage is environmental. “You are reducing your nutrient load on the oceans by a significant factor compared to a sea cage farmer, where all the discharge, all the waste material, goes directly into the ocean,” Mark Russell says. “Here you can collect the solid matter, significantly reduce nitrogen and phosphorus emissions and ensure no farmed fish escape into the wild.”

RAS technology mainly involves pumping, filtering, removing the CO2 and then degassing and oxygenating the water (see illustration).

“You imagine the water is your blood. It’s really going round and round the system the whole time,” Russell says. “The system runs on the same principles. You remove the waste materials from the return water with a mechanical filter. Then you pump it over to what we call a degasser, where we remove the carbon dioxide from the water and add oxygen. It’s very, very effective.

Danish Salmon keeps a constant rotation of fish through the different growth stages. As fish grow from eggs to full size, Russell’s crew moves them to bigger and bigger tanks. The biggest ones hold up to 35,000 salmon at one time.

Figure: Around and around the water goes, using the natural fall from the highest point from the tank at the top of the lift pump (23) to run through the CO2 degasser, the fish tanks and filters (4-5) and back to the lift pump. Two-thirds of the water goes out to the fish, and the rest goes back through the filters (9-10). Oxygen cones (12) add O2 directly to the water on the fish side. Illustration by L. Dopa

The technology of a land-based recirculation system

Photo: Oxygen cones replenish the fish tanks with O2 in the recirculating system, while a degasser removes the unwanted CO2 at the end of the line – like a body’s lungs do for a bloodstream.

Oxygen cones

Pumps for sustainable aquaculture

The natural fall of water and constant circulation from a giant lifting pump keeps water flowing around the tanks. Other pumps help in the processes of filtering, heating/cooling and oxygenating the water.

“More and more fish are actually produced on shore,” he says. “So there is a great future in going out to the world with sustainable pump solutions.”

Danish Salmon uses several types of Grundfos industrial equipment at its plant, including KPL lifting pumps, CR multistage inline centrifugal pumps for filtering, CM and TP pumps for heating, the NB pump for the oxygen cones and digital dosing pumps.

Mark Russell adds that ocean fishing is still a massive industry. “But there are only so many fish in the sea,” he says with a smile. “The stocks are declining. So with these systems, we can produce them more efficiently and sustainably, and get a product that is very competitive.”

Russell says the company uses Grundfos pumps in the land-based fish farming technology. “I have been fish farming for more than 20 years, starting in Scotland. The most reliable pumps we had were from Grundfos. When we got them second hand, we knew they would be in use for a long time.”